"When you buy it, they have this book and you say what school you go to and what year, and they write it down... " she said. "So if anyone else in my year level wants it, they're like, 'sorry, you can't have it'."

Amy is working part-time as a theatre usher to pay for her dress, which has cost more than $500. "It would be really devastating if she spent all this money on the dress and walked in and someone else had it," said her mother, Brenda.

Sophie Henon, area manager for Barbara Wilson, said: "We source what function it's for and check our formal book to make sure it's (the dress) not going to the same function."

At the time of purchase, details are faxed to the two other stores. With some dresses costing well over $1000, the style stakes are high.

Stores such as John Cavill and Veronica Lodge also offer the service for formals, debutante balls and bar mitzvahs. Typically people can purchase the same style but their colour and fabric choices are restricted.

John Mazaris, of Chapel Street boutique Memphis Dreams, has operated a registry for 14 years. "Not everyone can do it," he said. "Some styles are very popular. At least we guarantee the colour."

However, no registry system is infallible. In one case, an aunt sent to covertly purchase a barred Barbara Wilson gown was prevented by staff who recognised her. But she is said to have visited another outlet, fudged the event details, and purchased it there.